Trailering Magazine Archives - Trailering Maintenance
A "tab" that gives you the pick up...
The Talk about Trim Tabs
In the same way the aileron on the outside edge of a wing is designed to stabilize an airplane, trim tabs use these principles to smooth out and control the movement of a boat through the water. Many trailer boaters, however, may have never considered the need for trim tabs because they have no complaints about how their boat performs. This is a variation of the theme "ignorance is bliss" or "if it ain't broke, don't fix it."
There are, however, a number of tell tale signs that suggest an investment of trim tabs might be worth consideration:
* If you have to tell family members to move around in order to balance out the boat while underway.
* If the bow blocks your view for a long period of time while accelerating.
In each of these cases, the boat's "attitude" in the water is the issue. Every boat is designed with an optimum running attitude at which it will plane depending on the weight it carries and its speed. If there is a lot weight in the stern, the boat throws a larger wake because the stern is being pushed through the water at an inefficient angle. The preferred angle of the propeller is always parallel to the water flow. If the stern is "squatting," the propeller's alignment is too low in the water (see diagram). If passengers are gathered on one side of a trailered boat, you will notice listing to that side. Trim tabs have been proven to correct these common problems.
"We've specifically designed trim tabs for the trailered boat, the 17-23 foot crowd," says Tom McGow, Director of Client Services at Bennett Trim Tabs, one of the country's largest manufacturers of this specialized product. "In fact, a small boat needs them more than a large boat because it is more affected by the placement of passengers when loading and while underway as well as sea conditions."
McGow's idea pertains not just to passengers on the boat but those out of the boat as well. The trailer boater pulling water-skiers should pay attention to the amount of time that is required to get the person out of the water (no doubt the skier is doing this too) and the boat onto plane. With trim tabs set all the way down, the boat will pull the water skier out of the water faster. This has also been shown to work for boats operating at a slower speed pulling tubers. In both towing situations, the boat's attitude in the water is changed so that it is more efficient than were trim tabs not in place at all.
When a boat is on plane traveling at or near maximum speed, the bow will come down as the stern comes up. Upon reaching what is called "the running attitude, "the sharper edges of the hull are slicing through the water making the ride more comfortable. At the same time the boat is no longer operating in the transition between being stopped and planing called displacement running because now the wake has become smaller. Because the bow has now come down, the operator has a full view of the water ahead. It is here that a safety issue comes into play. In recent years there have been numerous accidents on the water because a powerboat ran over a swimmer or hit a log as a result of the operator not being able to see over the bow while moving at a slow speed. Because trim tabs extend beyond the stern and provide lift, the bow will sit at lower point than were no trim tabs in place.
A number of boat manufacturers have begun to offer trim tabs as either standard or optional features on a variety of trailerable models. It is a trend that is catching on throughout the industry. Boston Whales for example provides trim tabs as part of a standard package on 230, 260 and 290 Outrage series as well as on the 255,275 and 295 Conquest designs. Trim tabs are available on some Sea Ray and Key West models as well. But you need not buy a new boat to use trim tabs. Kits are available and installation doesn't require a degree in marine technology to perform.
"Next year we have a pair of trim tabs that are going to accommodate the entire range of trailer boat sizes," says Bennett's McGow. "That's when we introduce the M80 (for boats 17-20 feet) and the M120 series (designed boats 20-23 feet). We have trim tabs for sport boats that hit 40-60 mph and require two pistons to operate and we also build for bass and flats boats which have small transoms and require getting up on plane quickly because of the shallow water in which they operate. And we have a standard design that seems to fit most boats. There's a variety of choices, depending on the intended use."
A trim tab 101 rule is to buy a model with a length of at least one inch span (length of both tabs running parallel to the length of the transom) per foot of boat. An example would be installing a set of 9" X 12" trim tabs (total span of 24") which will accommodate a 20-foot boat. Because tabs are available in spans of 9", 12", 18" 24' and up while using a chord size (fore to aft measurement) of 9" or 12, there are many combinations available.
Manufacturers provide either manual or automatic trim tabs. With manual, the operator will adjust the position of the tabs with a joystick control placed in the cockpit. With an automatic adjustment, the operator takes the boat out and sets the tab positions for the most efficient performance. The automatic feature will remember these settings and adjust the tabs depending on the boat's attitude. In both cases, the purpose of the trim tabs is to assist the boat in staying on plane while running at optimum speed as well as a slower speed.
Since each trim tab operates independently, the operator can compensate for the boat listing to one side because the passengers have all moved to that side. By simply lowering the trim tab on the side with the most weight, the boat will return to its proper attitude in the water. It should be noted this in no way suggests it's acceptable to have all the passengers on one side while either at anchor or underway. But with this ability, the captain of the ship isn't going to have to decide who sits where.
Bennett Trim Tab's Mike McGow has another definition of what his product does: "We restore domestic tranquility." It can be said that comes with having a boat with good attitude too.